Method of processing used batteries

ABSTRACT

The invention relates to a method of processing used batteries, especially zinc-carbon and alkali-manganese batteries, in order to recover any usable or environmentally relevant substances, comprising the mechanical reduction of the initial material followed by the separation of the battery granulate thus obtained into a fine and a coarser fraction. The coarser fraction is further separated into a magnetic and a non-magnetic part, followed by principally wet chemical steps to sort out the fractions containing the individual useful or environmentally relevant substances and their separation.

FIELD OF THE INVENTION

The invention relates to a method of processing used batteries,particularly zinc-carbon and alkali-manganese batteries, in order torecover usable or environmentally relevant substances contained therein.

TECHNOLOGY REVIEW

Primary batteries are used in numerous self-contained, portable devicesas round, prismatic cells, and as button cells in large numbers.

Without a doubt, the breakthrough to modern, portable current sourceswas the configuration of zinc anodes as a cell box and the use ofmanganese dioxide as a positive electrode, and the idea of using a soliddepolarizer (manganese dioxide) in place of a liquid one, the soliddepolarizer being practically insoluble in the electrolyte solution.Depending on the battery system, ammonium chloride is used as theelectrolyte, possibly with added zinc chloride, or diluted potassiumchloride solution in batteries having zinc anodes. To suppressself-discharge, the zinc anodes are amalgamated with mercury salts.Additives such as copper and iron are only allowable in traces, while aspecific percentage of lead and cadmium in precisely matched proportionsof dimensions can contribute to the improvement in the zinc quality.

Primary batteries are only intended for one-time use. Up until a shorttime ago, after they had been exhausted, they were exclusively disposedof with normal household garbage or incinerated. This, however, causedenvironmental pollution. In recent times, these batteries are collectedseparately to an extent. However, destroying them in anenvironmentally-friendly manner causes great difficulties.

For a few years already, a focus of industrial battery production hasbeen to recover the used batteries.

A decisive impetus for this was not initially environmentalconsiderations, but economical reasons, i.e. recovery of raw materialssuch as zinc, ammonium and manganese.

Nevertheless, recycling makes an important contribution to environmentalprotection since, as mentioned, recycling prevents the organized as wellas arbitrary deposit of dangerous or valuable substances, respectively,from used batteries.

Different methods of material recovery from unusable batteries are knownfrom the art.

An example is FR 1,112,969. This document discloses a method ofrecovering metallic components from used dry cells, in which thebatteries are destroyed in the course of precarbonization, and thecontained chlorinated compounds are partially decomposed. The metalcomponents of the unburned proportion are mixed with carbon-containingmaterials and agglomerated. The agglomerates are then subjected to areduction treatment and subsequently an oxidation treatment, resultingin a manganese compound and zinc oxide. Zinc oxide is separated out ofthe combustion gases of the oxidation treatment. The chlorinatedcompounds remaining after precarbonization are destroyed during thereduction treatment and carried off as gaseous products.

In Indian Patent 127,714, the cells are opened and the reaction productsare removed. The zinc is washed with hot water and melted with theaddition of carbon at 800° C. This method is very work-intensive;moreover, no manganese is recovered.

In Japanese Patent 7,560,414, the reduced elements are dissolved in hothydrochloric acid, and low-valent manganese is obtained in the presenceof hydrogen peroxide. In Japanese Patent 74,106,419, the hydrochloricacid solution with ammonia is set at a pH value of 5, andiron-III-hydroxide is separated out. Whereas the batteries are reducedand subjected to wet screening and iron separation in the prestage inthis patent, in accordance with Japanese Patent 75,01,094, the used drycells are roasted for 8 hours at 750° C. in the presence of air and,following reduction, are dissolved to a fine powder in 20% hydrochloricacid.

A method of recovering zinc and manganese from exhaustedzinc-carbon-manganese batteries is known from Austrian Patent 381,808.In accordance with this method, the battery granulate, possibly afterprevious extraction, is melted with solid, carbon-containing reducingagents and iron carriers as added substances in a reduction vessel at1400°-1600° C., during which the zinc compounds contained in theresulting reaction gases, or metallic zinc and ammonium chloride arecollected, and manganese is recovered as zinc-free ferromanganese.

Swiss Patent 670,015 describes a method of disposing of used primarybatteries and recovering raw materials contained therein. This methodencompasses a dual-stage, thermal decomposition process. The batterygranulate is mechanically reduced as preparation for the thermaldecomposition process, moistened with water, and the pH value of themoist battery mass is set to a value above 12. Ammonia and water aredistilled off in a temperature range of 20°-150° C. In the second stageof the decomposition process, the batter mass is heated further, andmercury is distilled off in a temperature range of 350°-550° C. Aftercomplete cooling, the battery granulate, completely free from mercury,is again mechanically reduced. Subsequently, raw materials, mostly inthe form of oxides, can be sorted by particle size, specific weight andmagnetic behavior.

Swiss Patent 676,896 describes a method of disposing of and recoveringmaterial for unsorted, collected material from used alkali-manganese andzinc-carbon batteries, which method can also encompass small quantitiesof further battery types. After battery reduction, first the electrolytesalts are dissolved out of the mixture with water, and then gaseousammonia is expelled from the wash water due to a temperature increase bymeans of the addition of strongly alkaline substances. This lowers thesolubility of zinc, cadmium, mercury, copper, manganese and other metalsthat form ammonium complexes, and they precipitate out of the solution.The precipitated hydroxides or carbonates of these metals, or mercuryoxide, are removed from the waste water and can be processed togetherwith the fine fraction. The insoluble battery components are separatedinto a coarse fraction and a fine fraction by means of screening. Thelight plastic and paper parts are sorted out of the rough fraction bydensity, and iron granulate by means of magnetic separation. The powderyfine fraction is subjected to a thermal treatment. During this treatmentthe mercury is distilled out. After the thermal treatment, zinc isdissolved out of the residue with an aqueous solution. A separationbetween manganese and zinc is thus achieved, which permits furtherprocessing of the fine fraction into marketable products.

All of these methods of processing small batteries are associated withdifferent drawbacks. In most of the known methods, the batteries aresubjected to thermal treatment at higher temperatures in an oven. Duringthe treatment of these types of complex substance mixtures, as theyrepresent special garbage, particularly used battery waste, by heatingto above 1000° C., the formation of further, undesirable substances orsubstance mixtures with possibly environmentally relevant propertiescannot be ruled out.

However, there is no disclosure of the composition of the resultingwaste gases, or the chemical reactions in the oven and their products asa result of the thermal treatment of such complex systems.

However, the methods that have become known are not practical untillarger facilities are constructed. Technically, much can be accomplishedtoday, but what can actually be implemented is primarily dependent oneconomic efficiency.

SUMMARY OF THE INVENTION

It is therefore the object of the invention to create a method ofprocessing used batteries, particularly zinc-carbon and alkali-manganesebatteries, in order to recover usable or environmentally relevantmaterials contained therein, which method overcomes the drawbacks of theknown methods and permits the recovery, in an economical,practice-oriented form, of chemical elements present in the unusablecells, for example zinc and manganese, as well as other substancespresent therein or their compounds for which there is a technicalapplication. At the same time, a complete and reliable form of recoveryof environmentally relevant substances is intended to be permitted.Moreover, the method is intended to permit an economical processing ofused batteries, even on a small scale.

DETAILED DESCRIPTION OF THE INVENTION

This object is attained in accordance with the invention by a methodthat encompasses mechanical reduction of the initial material andsubsequent separation of the thus-obtained battery granulate into a finefraction and a coarser fraction, the coarser fraction being furtherseparated into a magnetic and a non-magnetic proportion, the methodfurther including subsequent, predominantly wet-chemical steps to sortout the individual fractions containing usable or environmentallyrelevant substances and separating them.

The method is explained in detail below.

The foreign parts of the battery granulate, which make up approximately1%, are sorted out on a primary screen and supplied to appropriatedisposal, depending on the nature of the foreign material. This can bedumping, incineration or some other processing.

Further, the nickel-cadmium batteries and mercury-containing buttoncells, classified as recyclable (in quantities of approximately 6-7%),are sorted out on the screen, either manually or, if possible,magnetically. Hence, only zinc-carbon and alkali-manganese batteriesremain for further processing. The sorted-out quantity of approximately92% is now subjected to a reduction process.

Following mechanical reduction in a closed screen system, the batterygranulate is first separated into two fractions, a fine fraction(particle size - 250 μm) and a coarser fraction.

The fine fraction, which is primarily composed of carbon, zinc dust andzinc compounds, as well as manganese compounds and ammonia compounds,makes up 60% of the total battery granulate and has approximately thefollowing composition:

    ______________________________________                                               zinc    14.3%                                                                 iron    4.57%                                                                 manganese                                                                             23.2%                                                                 nickel  0.3%                                                                  cadmium 0.2%                                                                  lead    0.1%                                                                  mercury 0.08%                                                          ______________________________________                                    

The remainder consists of water and other chemical compounds.

The coarser fraction, which in addition to iron also contains metalliczinc, small quantities of manganese compounds and other inorganicsubstances, as well as organic components such as paper and plastics, isbrought to a magnetic separator in order to separate out the iron. Thecoarse-grained fraction is composed of approximately 25% non-magneticand approximately 15% magnetic parts (with respect to the total batterygranulate).

The composition of the non-magnetic part is approximately:

    ______________________________________                                               zinc    37%                                                                   manganese                                                                              3%                                                                   iron    12%                                                                   nickel  5.7%                                                                  lead    1.8%                                                                  cadmium 2.0%                                                                  copper  0.35%                                                                 mercury 0.01%                                                          ______________________________________                                    

The remainder is composed of water and inorganic compounds, as well asplastics and paper.

Following washing, the magnetic fraction has approximately the followingcomposition:

    ______________________________________                                               iron   70.5%                                                                  zinc   1.9%                                                                   nickel 0.62%                                                                  mercury                                                                              0.04%                                                           ______________________________________                                    

This magnetic fraction can be supplied, for example, to the steelindustry after being washed out with water.

The non-magnetic, coarse-grained fraction is treated in the same manneras the fine-grained screening fraction, but separately because of thedifferent reaction times.

The fine fraction collected in water immediately after screening ispumped into a zinc-recycling system in order to prevent dust formation.In the system, all of the zinc and zinc compounds are brought intosolution as zincate. For this purpose, in accordance with the inventionthe pH value is set above 12 with sodium hydroxide solution. The settingof this pH value is moreover known to cause the aluminum chloridecontained in the zinc-carbon batteries to convert into ammoniumhydroxide.

Since, in accordance with the invention, the dissolution of the zinc indry batteries includes an exothermic reaction, the temperature of thereaction mixture increases by approximately 10° C. This temperatureincrease has a favorable effect on the evaporation of the ammonia, whichis concentrated to 30% in an ammonia washer. The obtained ammoniumhydroxide solution can be supplied to the chemical industry.

Following the reaction time, which, depending on the fraction, lastsapproximately 1 to 2 hours, but must be sufficiently long in any case inorder to convert the total ionic and metallic zinc into zincate, thestirring mechanism of the system is shut off; in the coarse fraction,plastics, paper, sealing compounds and other swimming, primarily organiccomponents are skimmed off and supplied to further purification. Thispart of the coarse-grained fraction is practically free from pollutantsafter purification, and can be conditioned for dumping in accordancewith the suitable consolidation method.

The remaining reaction mixture, which contains the heavy,water-insoluble components such as manganese compounds, carbon, metalsand metal compounds and the zinc dissolved in the strongly basic range,is filtered off. The liquid phase, which, even after filtering, stillcontains colloidally-dissolved manganese-oxygen compounds, is filteredvia a sand filter. Zinc hydroxide precipitates out of this phase due tothe pH setting. In accordance with the invention, the pH of 11 hasproven very effective, because at this pH value zinc oxide is composedof very easily filterable crystals. The obtained zinc hydroxide, whichstill contains 0.2 weight-% lead and 0.02 weight-% manganese (withrespect to the drying substance), is appropriately treated for furtheruse.

For example, to obtain zinc and for galvanic zincking, the zinchydroxide is dissolved as sulfate in sulfuric acid, and lead is to beseparated out as water-insoluble lead sulfate.

The alkaline dissolution of zinc from dry batteries in accordance withthe invention, and the resulting ammonia removal further have theadvantage that the poisonous metal components, such as cadmium,manganese, nickel and copper, as well as very volatile mercury chlorideconvert to metal oxides, thereby reducing environmental pollution bymercury and other metals and their compounds.

The part of the two fractions that is insoluble in the alkaline range isnow supplied together to further processing.

In a closed reaction container, the sludge is slurried with water, withthe reaction temperature being maintained below 15° C., and a pH valueof 1 is set with concentrated hydrochloric acid. At this pH value, allmetals and metal compounds present in dry batteries are dissolved. Theactive carbon located on the surface of the reaction mixture is skimmedoff and washed out, and the wash water can be set at the pH valuesuitable for a sulfide treatment, possibly with sodium hydroxidesolution.

It has been seen in practice that this carbon is free from heavy metalions after two washings. It can possibly be used for air-filter systemsin industry after being dried. Likewise conceivable is use in thebattery industry. Of course, this active carbon can also be suitable forburning.

The clear, acidic solution obtained after separation contains, inaddition to manganese-II-chloride, other chlorides such asiron-II-chloride and cadmium-II-chloride, and mercury compounds.

Following is a detailed description of the composition of the manganesecompounds that have resulted both during battery discharge and, mostnotably, after shredding, when the zinc is dissolved as a consequence ofthe reduction reaction. In accordance with the formula, theelectrochemical reaction in cells, in which the chemical energy is freeas electrical energy, and the reaction during dissolution of the zinc inthe alkaline range, in which chemical energy becomes free as heat, canbe summarized in the following manner:

    Zn+2 MnO.sub.2 +2 H.sub.2 O--Zn (OH).sub.2 +2 MnOOH

In the two arrangements, manganese dioxide converts in the end into lowmanganese oxide that is insoluble in the alkaline range. These oxides,in contrast to manganese dioxide, are practically insoluble in thealkaline range, as shown by the analysis of the alkaline zincatesolution.

A separation of manganese-II-chloride as manganese dioxide in the acidicrange can be effected electrochemically, along with other heavy metalions, in accordance with CH 548,953, or manganometrically according toA. George (Ann. Chim. phys. [3]66 [1862]153/61, 159/60).

The course of the reaction runs magnometrically according to theempirical equation:

    3 Mn.sup.2+ +2 MnO.sub.4.sup.- +2 H.sub.2 O--5 MnO.sub.2 +4 H.sup.+

The potassium permanganate needed for the above reaction can be producedfrom a part of the manganese dioxide obtained in accordance with thismethod by means of melting with an approximately stoichiometric quantityof KOH under the influence of oxygen (W. Baronius, G. Marcy (Chem. Tech.[Leipzig] A8 [1966] 723/7).

Mn^(II), which is very difficult to oxidize, is easily incorporated intothe manganese dioxide, the majority of which precipitates outimmediately. For this reason, the formal degree of oxidation x of theMnO_(x) phase is always within "two." The values of x are very dependenton the representation conditions. With a pH value of 2 and a slighttemperature increase to 40° C., the theoretical value of 2 isapproached.

A Guyard (Chem. News 8 [1863]292/3; Bull. soc. chim. France [2]1 [1864]

Manganese dioxide is filtered off and washed out twice with water. Afterthe foreign ions have been removed by means of washing, the pH value ofthe wash water can be set to 7 with sodium hydroxide solution. Themanganese dioxide produced in this way can be used as a cathodedepolarizer in dry batteries, or supplied to the chemical industry.

The acidic solution obtained after filtering off of the manganesedioxide is brought to a pH value that is suitable for further sulfidetreatment with sodium hydroxide solution. The precipitated sulfides,among them mercury sulfide, are dumped after consolidation.

A mercury contamination of the zinc hydroxide and the manganese dioxidewas not detected. Mercury compounds which precipitated as sulfides inthe end were detected exclusively in the acidic solution after theprecipitation of the manganese dioxide.

In the recovery of zinc and manganese from used batteries, these twoselected methods are element-specific, and no other elements present indry batteries can participate in the reactions. Because ofalready-known, suitable reaction conditions, a mixed crystal formationcan be nearly completely suppressed during precipitation.

In this method of using the used batteries, which is based onwet-chemical steps, reactions and steps are selected that do not requirea temperature increase, in contrast to already-known, thermal methods.The work space hazard and emissions are the only factors that must beconsidered. For this purpose, mechanical reduction and screening takeplace in a closed system, and the exhaust air is purified by way of afilter system, and finally by means of an active carbon doped withiodine and sulfur. Because of this filter system, the exhaust air isfree from particles as well as any volatile battery components. Thedissolution of the sludge after zinc separation is likewise performed ina closed system, in which the exhaust air is carried off by way of anexhaust air purification system, as described above.

What is claimed is:
 1. A method of processing used batteries to recoversubstances contained therein, comprising:mechanically reducing usedbatteries into battery granulate; separating the thus-obtained batterygranulate into a fine fraction and into a coarser fraction; separatingsaid fine fraction and said coarser fraction into a magnetic part and anon-magnetic part; chemically separating zinc from a non-magnetic partby adjusting the pH value of a solution of said non-magnetic part above12 to dissolve all zinc; removing ammonia released by pH value above 12;filtering said solution; adjusting the pH value of the solution to 11;and filtering a zinc-containing precipitate.
 2. The method as set forthin claim 1, including separating carbon after said zinc-containingprecipitate has been removed, by adjusting the pH to a value of 1, andfiltering the carbon from the surface of the solution.
 3. The method asset forth in claim 1, including separating manganese by electrolysis. 4.The method as set forth in claim 3, including separating mercurycompounds by sulfide precipitation.
 5. The method as set forth in claim1, wherein each substance is recovered without additional heating. 6.The method as set forth in claim 1, including further purifying eachrecovered substance.